For example, a reactor for a vehicular booster circuit has been known which includes a resin cover (also called a bobbin) that covers the circumference of an annular magnetic core, and a coil provided around the outer circumference of the resin cover.
As disclosed in JP 2014-199872 A and JP 2012-049269 A, according to such a type of conventional reactors, the entire reactor is housed in the casing, and a filler is applied and solidified between the reactor and the casing.
In the case of, for example, vehicular reactors that have a large amount of heat generation when a current flows, it is necessary to improve cooling efficiency. For that purpose, it is proposed to make the coil surface exposed so as to allow such a portion to be directly in contact with a cooling medium, such as a cooling oil or an air. For example, US 2014/266527 A and JP 2015-046481 A disclose that oils are applied to the reactor for cooling, and according to this type of reactors, elimination of the filler improves the cooling efficiency.
According to conventional reactors that utilize the filler, the filler eliminates a gap between conductive wire portions that form a coil, and a gap between the coil and the resin cover around the core, and thus generation of noises due to vibrations of the conductive wire of the coil and the resin cover when a current flows through the reactor is suppressed. In the case of reactors that do not utilize the filler, however, such an effect is not accomplished, and thus vibrations and noises may be generated.
In general, according to reactors, in order to connect the coil to an external electric circuit, a drawn portion of the coil end portion is connected to the terminal of the electric circuit by, for example, welding. In the case of reactors that do not utilize the filler, however, stress may be applied to a connection portion between the coil and the terminal due to vibrations of the coil, possibly causing a break-down in a long-term use.